1. Technical Field
The disclosure relates to an auto-selecting holding current circuit, and more particularly to an auto-selecting holding current circuit capable of being coupled to different Triodes for Alternating Current (TRIACs).
2. Related Art
With the rapid development of science, technology and economy, people have higher and higher requirements on the quality of life, which, however, leads to the gradual exhaustion of crude oil reserves. In recent years, with the rise of the environmental protection awareness, various green energy industries have attracted global attentions, in which an illumination-related energy saving requirement becomes one of the important indexes.
Generally speaking, power consumption of illuminators is usually too high. When strong illumination is not needed, energy can be saved effectively if the illumination of the illuminator can be lowered. Common dimmers include TRIAC dimmers, electronic dimmers, and remote control dimmers (such as infrared or radio frequency remote control dimmers).
The TRIAC dimmer mainly includes a TRIAC for changing the input power of a light, and one of the TRIAC features is the holding-current value. When the TRIAC is triggered, the TRIAC maintains a conducting state. When the current flowing through the TRIAC drops below the holding-current value, the TRIAC is closed (or cut off). To decrease the luminance of the illuminator, both the input voltage and the input current of the illuminator are decreased, which causes the TRIAC to be closed earlier than expected since the current flowing through the TRIAC is smaller than the holding-current value, and further causes the TRIAC misfire and illuminator to flicker. In order to solve the above problems, a conventional method for adding a bleeder circuit (or dummy load) in the TRIAC dimmable LED driver is adopted, so that the current flowing through the TRIAC is higher than the holding-current value even when the TRIAC current is decreased, therefore maintaining normal functions of the TRIAC. A common bleeder circuit transmits an extra current extracted from an input voltage to the TRIAC by connecting a constant resistor to the input voltage in parallel, so that the current flowing through the TRIAC is greater than the holding-current value, therefore maintaining the TRIAC turned-on. However, the above method fails to achieve an effect of dynamically compensating for the exact amount of current that the TRIAC lacks. Therefore, a conventional adaptive bleeder circuit is provided to dynamically satisfy the current needed by the TRIAC. However, the adaptive bleeder circuit is merely applicable to the TRIAC having a specific holding-current value. The same adaptive bleeder circuit is not applicable to another TRIAC having a different holding-current value. Therefore, the conventional adaptive bleeder circuit is inconvenient in use.